Added FilterTuple implementation of CombinedFilter.

Simply wraps three different values in a single implementation of CombinedFilter.
Factored ParquetFileMetadata out of S3AvroIndexedParquetRDD.

ParquetFileMetadata is a wrapper class that contains all the information we need,
for extracting schemas or file metadata, or creating partitions, from a parquet file.
wip reording constructors to RangeIndex.
Passing tests for S3AvroIndexedParquetRDD.